This invention relates to an improvement on a light control apparatus for an automobile which is designed to control the brightness of the illumination light illuminating, for example, a panel board of a dash panel of an automobile.
An automobile light control apparatus of this type is known as shown in FIGS. 26 and 27. This prior art will be described hereunder.
1 denotes a mother board of a printed board on which a circuit pattern is printed. Soldered at appropriate circuits are electronic parts 2 of an oscillating circuit, a power transistor 3 of an electric power driver circuit, and a rhoostate or varible resistor 4 for varying the duty of switching. Lead wires 5 from this mother board 1 as well as a shaft 4a of the variable resistor 4 are led out from a casing (not shown). The lead wires 5 are connected to an electric power source and illumination lamp, thereby enabling to vary the duty of self-oscillating switching in order to adjust the voltage to the illumination lamp for controlling the brightness of the illumination lamp.
As seen in the above, the conventional automobile light control apparatus uses a variable resistor which is already completed as a variable resistor. Because of the foregoing, it has such a disadvantage as the casing thereof is necessarily made large which eventually requires a large installation space and high costs.
Moreover, since almost no consideration is paid to a temperature to the power transistor of the electric power driver circuit, the prior art apparatus has much possibility to go out of order. In addition, since the lead wires led out of the mother board are connected to the lead wires from an electric power source and illumination lamp, an intermediate connector is required.
The present invention was accomplished in order to remove the above mentioned disadvantages.